1. Field of the Invention
The present invention concerns an organic electroluminescent device and a display device and, more in particular, it relates to an organic electroluminescent device using an anode as a reflection electrode and a display device using the same.
2. Description of the Related Art
In an organic electroluminescent device utilizing electroluminescence (hereinafter referred to as EL) of an organic material (so-called organic EL device), an organic layer formed by stacking an organic hole transport layer or an organic light emission layer is disposed between an anode and a cathode, and it has attracted attention as a light emission device capable of emitting light at high luminosity by low DC voltage driving.
FIG. 5 is a cross sectional view showing an example of a constitution of the organic electroluminescent device described above. An organic electroluminescent device 101 shown in the drawing is disposed on a transparent substrate 102, for example, formed of glass and has an anode 103 disposed on the substrate 102, an organic layer 104 disposed on the anode 103, and a cathode 105 disposed on the organic layer 104. The organic layer 104 has a constitution of stacking a hole injection layer 104a, a hole transport layer 104b, and an electron transporting light emission layer 104c successively from the side of the anode 103. In the organic electroluminescent device 101, electrons injected from the cathode 105 and holes injected from the anode 103 are re-combined in the light emission layer 104c, and a light generated upon re-combination is taken out by way of the anode 103 or the cathode 105. The organic electroluminescent device also includes those having a constitution of stacking a cathode, an organic layer and an anode successively from the side of the substrate.
In an active matrix type display device in which a thin film transistor (hereinafter referred to as TFT) for driving each of organic electroluminescent devices is disposed on a substrate, it is advantageous for improving the opening ratio of a light emission portion to adopt a top emission structure of taking out emitted light generated in the organic electroluminescent device from the side opposite to the substrate. Further, improvement of the opening ratio can decrease the density of current applied to each of devices for obtaining necessary luminance to extend the life of the device.
Then in the organic electroluminescent device 101 of the constitution, for example, shown in FIG. 5, the anode 103 disposed on the side of the substrate 102 is used as a reflection electrode and the cathode 105 is used as a transparent or semi-transparent electrode. Then, for taking out the emitted light efficiently from the side of the cathode 105, it is necessary to constitute the anode 103 with a material of high reflectance.
For the material constituting the anode 103, it has been proposed to use, for example, silver (Ag) or a silver-containing alloy (refer to JP-A Nos. 2003-77681 and 2003-234193). Further, JP-A No. 2003-234193 also proposes the use of an aluminum (Al) alloy comprising copper (Cu), palladium (Pd), gold (Au), nickel (Ni), or platinum (Pt) as an secondary ingredient metal.